Re: [Qemu-devel] test-filter-mirror hangs

[Jason Wang]

On 2019/1/24 下午5:47, Markus Armbruster wrote:
> Please cc: me on QMP issues.


Ok.


> Jason Wang <address@hidden> writes:
>
> > On 2019/1/24 上午3:53, Dr. David Alan Gilbert wrote:
> > > * Jason Wang (address@hidden) wrote:
> > > > On 2019/1/22 上午2:56, Peter Maydell wrote:
> > > > > On Thu, 17 Jan 2019 at 09:46, Jason Wang<address@hidden>  wrote:
> > > > > > On 2019/1/15 上午12:33, Zhang Chen wrote:
> > > > > > > On Sat, Jan 12, 2019 at 12:15 AM Dr. David Alan Gilbert
> > > > > > > <address@hidden  <mailto:address@hidden>> wrote:
> > > > > > >
> > > > > > >        * Peter Maydell (address@hidden
> > > > > > >        <mailto:address@hidden>) wrote:
> > > > > > >        > Recently I've noticed that test-filter-mirror has been hanging
> > > > > > >        > intermittently, typically when run on some other TCG architecture.
> > > > > > >        > In the instance I've just looked at, this was with s390x guest on
> > > > > > >        > x86-64 host, though I've also seen it on other host archs and
> > > > > > >        > perhaps with other guests.
> > > > > > >
> > > > > > >        Watch out to see if you really do see it for other guests;
> > > > > > >        it carefully avoids using virtio-net to avoid vhost; but on s390x it
> > > > > > >        uses virtio-net-ccw - could that hit the vhost it was trying to avoid?
> > > > > > >
> > > > > > >        > Below is a backtrace, though it seems to be pretty unhelpful.
> > > > > > >        > Anybody got any theories ? Does the mirror test rely on dirty
> > > > > > >        > memory bitmaps like the migration test (which also hangs
> > > > > > >        > occasionally with TCG due to some bug I'm sure we've investigated
> > > > > > >        > in the past) ?
> > > > > > >
> > > > > > >        I don't think it relies on the CPU at all.
> > > > > > >     I have no idea about this currently, but Jason and I designed the
> > > > > > > test case.
> > > > > > > Add Jason: Have any comments about this ?
> > > > > > I can't reproduce this locally with s390x-softmmu. It looks to me the
> > > > > > test should be independent to any kinds of emulation. It should pass
> > > > > > when mainloop work.
> > > > > I've just seen a hang with ppc64 guest on s390x host, so it is
> > > > > indeed not specific to s390x guest (and so not specific to
> > > > > virtio-net either, since the ppc64 guest setup uses e1000).
> > > > >
> > > > > thanks
> > > > > -- PMM
> > > > Finally reproduced locally after hundreds (sometimes thousands) times of
> > > > running.
> > > >
> > > > Bisection points to OOB monitor[1].
> > > >
> > > > It looks to me after OOB is used unconditionally we lose a barrier to make
> > > > sure socket is connected before sending packets in test-filter-mirror.c. Is
> > > > there any other similar and simple thing that we could do to kick the
> > > > mainloop?
> > > Do you mean the:
> > >
> > >       /* send a qmp command to guarantee that 'connected' is setting to true. */
> > >       qmp_discard_response(qts, "{ 'execute' : 'query-status'}");
> >
> > Yes.
> >
> >
> > > why was that ever sufficient to know the socket was ready?
> >
> > It was suggested by Fam, I don't remember the details. Can we make
> > sure all pending events has been processed (UNIX socket was set to
> > connected) after query-status is returned with an non OOB monitor?
> I'm afraid I lack context.  Which socket are you talking about?  The
> test has at least the QMP socket, the send_sock[], and recv_sock.  What
> exactly are you trying to accomplish?


I mean recv_sock. If mirror tries to send a packet to it before its 
is_connected is set to true, packet will be dropped.


> By the way, mkstemp(sock_path) followed by unix_connect(sock_path, NULL)
> looks rather fishy.  Why create a temporary file only to create a Unix
> domain socket right over it?


I vaguely remember passing fd created by unix domain socket doesn't work 
when the test is introduced. So my understanding is the author needs a 
way to create a unique file name which will be used b Unix domain socket 
at that time.



>   Why is ignoring errors a good idea?


I don't get, which error is missed, it checks the return value of both 
mkstemp() and unix_connect().

Thanks